In the art of pressure fluid operated percussion tools it is desirable to control the impact blow energy as well as the blow frequency which is generated for transmission to the tool workings. In particular in the art of rock drilling with percussion drills it has been determined that a rock formation having a particular hardness or compressive strength can be penetrated in the most efficient manner at a particular impact blow energy value taking into consideration the configuration and size (diameter) of the percussion bit. U.S. patent application Ser. No. 621,935, filed Oct. 14, 1975, in the name of James R. Mayer and Dieter K. Palauro, and having the same assignee as this application, provides a more detailed discussion of this desideratum in the art of percussion drilling.
This invention pertains to improvements in a type of hydraulic oscillator adapted for percussion drilling whereby variable impact blow energy and blow frequency may be obtained and easily and conveniently controlled to select the desired hole formation (penetration) rate for a particular type of workings. The general type of hydraulic percussion tool mechanism which may be improved by the subject invention includes the type of apparatus disclosed in U.S. Pat. Nos. 3,896,889; 3,903,972; and 3,911,789.